In the rotating vector model (RVM) of [1]}, the radio radiation is beamed along the field lines and the plane of polarization is determined by the orientation of the magnetic field as it sweeps past the line of sight. The position angle (PA) as a function of pulse longitude, \(\phi \) , can be expressed as
\({\rm PA} = {\rm PA}_{0} +{\rm arctan} \left( \frac{{\rm sin}\alpha \, {\rm sin}(\phi - \phi _0)}{{\rm sin}\zeta \, {\rm cos}\alpha - {\rm cos}\zeta \, {\rm sin}\alpha \, {\rm cos}(\phi - \phi _0)} \right)\) 
